Rotary expansible drill bits



Oct. 4, 1955 A. w. KAMMERER, JR

ROTARY EXPANSIBLE DRILL BITS Filed April 1, 1954 d 4- d 1 3 1g WW ZZfiZZ rW T L i g A? 7 w o "I r! v 1. I}. 1 4 ud 0 7 8 c 1 22$ 223 i? 4 j a a a J 3 H 5:; g 5 i? w 6 $744. 1 I w I a w BY 953 41 M United States Patent ()fifice Z ,7 l 9 ,701 Patented Oct. 4, 1 955 2.11 .101 ROTARY EXPANSIELE EM ITS.

Archer W. Kammerer, 111., Fullerton, assignor, by d ec nd. ne. s nment a iq ary O T9 C9 3 P ar, Hua Pa k i a qor r fign of Ca ifornia i Application April 1, 1954, Serial No. 420,342

0 C aim, (c 25 The present invention relates to drill bits, and more particularly to rotary bits ofthe expansible type for drilling or reaming bore holes below well casin or other well conduits, to a diameter which is greater than the inside of the casing through which the bits are capable of passing.

Expansible drill bits are known in which the cutters are expanded laterally outward and locked in such expanded position through the agency of a mandrel telescopically arranged in the body of the drill bit. The mar drel is moved down relative to the body to lock the cutters in an outward position. Upward movement of the mandrel relative to the body releases the cutters and enables them to be moved inwardly toward retracted position. i

Certain disadvantages are associated with bits of the above type'which have been heretofore produced. A downward forcemust be maintained on the mandrel to hold it in its locked position, in order to secure the cutters in their outwardly expanded position. When this downward force is eliminated, "which may occur as a result of the cutters no longer engaging the formation shoulder, the body and cutters can move or, drop down with respect to the mandrel, which is the same as producing relative elevation of the mandrelin the body and shifting of the mandrel to an'unlockedposition, allowing the cutters to retract, at least partially. It becomes necessary to reshift the mandrel down in the body to again lock the cutters in their fully expanded position, but before this occurs, a length'of undergauged hole might bedrilled, i

' Accordingly, it is an object of the present invention to provide an improved expansible type of drill bit, in which the cutters'are held locked in their fully expanded position despite the relieving of the cutters of drilling weight, such 'as occurs when the cutters are elevated above the formation shoulder on which they have been operatmg, or the cutters enter a cavity, or the like, in'the bore hole. i

Another object of the invention is to provide an improved expansible type of drill bit embodying a locking mandrel telescoped in the bit body, in which the'man'drel is maintained in its locking position in the body to hold the cutters in their outward expanded condition, despite the absence of drilling weight on the cutters.

A further object of the invention is to provide an expansible type of drill bit embodying a locking mandrel telescoped with respect to the bit body, in which the mandrel is maintained releasably and in a positive manner in its locking relation holding the cutters in their outwardly expanded condition during the absence of drilling weight on the cutters.

Still another object of the invention is to provide for the releasable holding of the locking mandrel in'its locked relation to the cutters, and to also provide for the releasable maintenance of the mandrel in its ineffective position with respect to the cutters of the rotary drill bit This invention possesses many other advantages, and has other objectswhich may bemade morec lea rly apparwt from? e sa n 9 ev ra arm. whic t may be embodied. Such forms are shown in the drawings m n e a r n p r i he Pre ent pes fi fibril These Pi' w l n w e de ed n deta l ustrating the general principles. of the inventionrbut it is to be understood at snqh'smi s dess t on. is n t to be taken T a i ii ss. en e 1 QQP? 9 e. nvettion is best defined by the appended claims.

Referring tothe. drawings:

Figure l is a longitudinal section; through an expansible rotary drill bit disposed within a well bore, taken generally along the line 1 -1 on Fig. 4, with the Pa i of the drill bit in retracted position for lowering in the well bore; I

Fig. 2 is a view similar to Fig. l-, with parts of the drill bit in their fully expanded position; i

Fig. 3 is a fragmentary enlarged longitudinal sefiiion through a portion of the drill bit shown in Fig. 1;

Fig. 4 is an enlarged cross-section taken along the line 4 4 on Fig. 1;

Fig. 5 is a view similar to Fig. 3, disclosing a modified form of releasable detent device.

As shown in the drawings, the expansible rotary drill bit A is attached to a string of, drill pip'e B by means of which it is lowered in the well borej to the point at which enlargement of the bore hole is to commence. The bit is capable of enlarging the bore hole by producing "and operating upon a formation shoulder C, as hereinafter described.

r The upper end of the bit consists of a driving mandrel 11 whose upper pin 12 is threadedly connected to a sub 13, forming the lower end of the drill pipe string B. This mandrel includes an upper kelly or drill s'temni'eniber 14 slidably spline'd' to' the main body 15 "or the bit in any suitable "manner, such as disclosed in Pateiit 2,466,991. The mandrel 14 has alimited range of lori gitudinal movement within the body, its up'ward moveinent being determined "by engagement'of' an'ext'fnal shoulder '16 on'the' kelly with a; retainer ring 17 suitably secured to theu'pper end of the body 15, as by the use or welding material 18.

The body 15 has'a plurality of expansible parts mounted on it", comprising opposed cutter supporting mmbers19, 19 pivotally' carriedon pivotor hinge pins 21, 21" suitably secured to the body. Each cutter supporting member consists of a depending leg 23 having a bearingsun porting pin 24 inclined "inwardly and downwaidly and on which is 'rotatably mounted a rollenside cutter '25 Anti-friction roller and ball-bearing elements 26, 27 are preferably placed between each cutter ZSan'd bearing pin 24; the roller'b'earings 26 transmitting 'radialthr'ust'sjand the ball bearings 27" bo th radial andaxiabthrusts'. "The balls 27 are iris'ertable between thejpin' 24 and cutter25 through a hole 28', which is then closed 'bya plug 2 9. Each cutter supporting member 'i9'a1so includes upwardly extending arni 30"against which au elast ic expander 31'be'ar's." expander is in'the form of a compressed coil spring received within ar'etain'r pocket in the body exerting its force against the arm 30 kelly 14 and is provided with a lock portion 47. The latter is movable from an upper position in transverse alignment with inner supporting member recesses 36, permitting retraction of the cutters, to a lower position opposite lugs 37 formed on and projecting inwardly from the supporting member legs 23, preventing retraction of the cutters 25.

The tubular member 35 is connected in swivel fashion to the kelly 14 to permit relative arcuate or rotary movement therebetween. However, the kelly and tubular member are movable together for longitudinal movement in both directions. All this is accomplished by providing a shoulder 56 on the tubular member containing an external toroidal raceway 57 receiving bearing balls 38 that are also ridable in an opposed internal raceway 39 formed in the kelly 14. The balls 38 are insertable through a hole 40 extending through the kelly shoulder 16, and, after having been mounted in place within the raceways 57, 39, this hole can be closed by a suitable plug 41 which is prevented from moving out of the hole by the main body 15 of the bit.

The upper portion 35a of the tubular member 35 is piloted within the fluid passage 42 through the kelly 14, and has its end 35b flaring upwardly and outwardly to guide a ball 43, or corresponding element, into the central passage 35c through the tubular member 35. Fluid pumped down the drill string B will flow through the kelly pin 12 and into the central passage 35c. It is prevented from flowing around the exterior of the tubular member 35 by a suitable packing 44 disposed between the upper portion 35a of the tubular member and the kelly 14 adjacent the upper end of the tubular member shoulder 56.

The arrangement between the tubular member 35 and kelly 14 is such that both downward and upward movement is transmitted between the kelly 14 and tubular member 35 from one raceway 57 or 39, through the ball bearing elements 38, to the other raceway 39 or 57. In this manner, the kelly 14 and tubular member 35 are caused to move jointly in both longitudinal directions, but they are able to partake freely of relative move ment therebetween.

The mandrel 11 is disposed initiallv in its upper position with respect to the main body 15 of the bit and the supporting members 19, with its shoulder 16 disposed above a guide 48 resting on the body 15. This guide 48 serves as an upper bearin for the tubular mandrel member 34, whose lower end is slidable within a lower bearing guide 49 below the luns 37, whi h is i te ral with or secured to the main body of the bit. The two guides 48, 49 form a spaced two-point sup ort for the mandrel member 35 and assist it in resistin inward movement of the cutter le s 23 to retracted position during the reaming or cutting operation,

Circulating fluid can pass downwardly throu h the string of drill pine B and throu h the tubular mandrel 11 for ejection from its lower dischar e nozzle 35 and onto the cutters 25, to c eanse them of cu tin s and fl sh the latter from the dri lin area to the too of the well bore. This circulating fluid is also availed of to unlatch the cutter su orting members 19. in the event it is desired to hold them positively in retracted position.

The cutters may be retained initially in retracted ositions against the ex ansive forces of the springs 31 by means of a trip device. This device includes a holdin plate or member 78 secured to the lower end of a central rod 79, whose upper end proiects into the tubular member passage 35c. A head 80 is secured to the upper end of the rod, which has substantial clearance therearound. in order to allow fluids to pass upwardly into the central passage 35c and into the drill string B. The holding member 78 has spaced holes 82 in its outer portion for receiving the lower ends 29a of ball bearing plugs or pins 29 which hold the cutter bearing balls 27 in operative position.

When the holding device 78 is disposed over the pins 29, the cutter supporting members 19 are prevented from expanding under the influence of the springs 31, thereby holding the cutters 25 in retracted position. It is to be noted that the pins 29 are inclined initially in a downward and outward direction, so as to prevent the holding member 78 and the rod 79 connected thereto from moving downwardly until purposely released, which downward movement would allow outward expansion of the cutters 25. Such release can occur as a result of fluid pressure acting downwardly on the ball 43, which can rest on the head 80.

During lowering of the cutting tool to the point at which the reaming operation is to begin, the holding device 78, 79 retains the cutters 25 in retracted position. During this lowering operation, fluid may flow upwardly around the holding device rod 79 and around the head 88 into the tubular member passage 350.

When the point in the well bore has been reached at which the reaming operation is to begin, the pumps at the top of the well bore are started and drilling fluid pumped down the drill string B. The ball is then forced down through the passage 35c onto the head 80. Since the diameter of the ball is preferably equal to the diameter of passage 35c, it substantially closes the passage to downward flow of fluids, which allows the pumps at the top of the well bore to exert a pressure on the fluid in the drill string B and tubular member. This pressure acts downwardly on the ball 76, which correspondingly exerts a downward force on the holding device 79, 78, shifting the latter in a downward direction off the pins 29, and the ball 76 and rod 79 completely out of the passage 35c. The pins 29 are thereby released, allowing the springs 31 to expand the cutters 25 outwardly, while at the same time the passage 350 is free from restrictions, which allows fluid to be pumped through its lower nozzle 35d onto the cutters.

In the operation of the device, the tool A is mounted on the lower end of the drill string B, with its parts held in retracted position by the latch or trip device 78, 79, as shown in Fig. 1. In this position of operation, the mandrel 11 and its kelly 14 are in an upward position with respect to the body 15, as determined by engagement of the kelly shoulder 16 with the body retainer ring 17. With the mandrel in this position, its lock portion 47 is elevated above the lugs 37 on the cutter supporting members 19, being received within the inner recesses 36 in the supporting members, which permits the latter to be held inwardly against the action of the expander springs 31.

The tool is lowered through the well casing, and upon reaching the position in the well bore at which the drilling operation is to begin, the pumps are started at the surface of the well bore, the fluid under pressure in the drill string and bit A forcing the trip device 78 ofi the pins 29, releasing the cutter su porting members 19 for outward expansion under the influence of the springs 31.

The drill strin B is th n rot ted to rotate the main bit hodv 15 throu h the sn ined kelly and body connection, the expander sprin s 31 forcing the arms 38 inwardly and the cutters 25 outwardly against the formation. Rotation is continued wi hout moving the drill string longitudinally until the side c tters 25 enlar e the diameter of the h le to the maximum extent, as determined by the eventual abutting of the supporting member stop shoulders 33 with the companion body stop shoulders 34. Thereafter. the drill string is lowered to cause the formation shoulder C. produced in the well bore by the cutters 25 under the action of the expander springs 31, to support the cutter members 19 and body 15, and prevent their downward movement.

Since the body 15 cann t move downwardly, drilling weight imposed on the drilling string B shifts its connected mandrel 11 downwardly Within the body until the lower end 58 of the kelly 14 engages the upper guide 48.

This downward movement also shifts the tubular member 35 downwardly, because of the interlocking ball thrust bearing 37, 38, 39, to position the mandrel or tubular member lock portion 47 opposite and in alignment with the lugs 37 on the inner portions of the cutter supporting members 19, providing a positive lock by preventing inward movement of the cutters. So long as down weight is imposed on the drill string B, and the cutters 25 rest on the formation shoulder C, the cutters are prevented from moving inwardly by engagement of their lugs 37 with the mandrel lock portion 47. It is also to be noted that further outward movement of the cutters beyond the predetermined maximum reaming diameter is prevented by contact between the supporting member shoulders 33 and the body shoulders 34, through which the drilling weight is transmitted to the roller cutters 25, thus relieving the hinge pins 21 of this load.

Drilling is continued by rotating the drill bit and imposing the proper drilling weight on the cutters to cause their removal of the formation material and reaming of the hole in a downward direction for the desired extent or length. When the drill bit is to be retracted and removed .to the top of the well bore, all that needbe done is elevate the drill string B, which moves the side cutters 25 above the formation shoulder C, allowing the body 15, together with the cutter supporting members 19, to move downwardly with respect to the mandrel 11. This action re-positions the mandrel lock portion 47 opposite the supporting member recesses 36 and above their lugs 37, because of the ball bearing coupling 38, permitting inward swinging of the cutters 25 and their supporting members 19 when the tool passes back into a well casing (not shown), upon elevation of the drill string B. The cutters 25 and their supporting members 19 will ride the wall of the casing during elevation of the string until the tool is removed from the top of the well bore.

With the apparatus described above, the locking mandrel 11 remains in its downward position, such asdisclosed in Fig. 2, to positively hold the cutters 25 in their outwardly expanded condition, so long as down or drilling weight is being imposed upon the apparatus. However, should the drill string B and the mandrel 11 be elevated, then the lock 47 on the latter would be raised above the locking lugs 37 and the cutters might be retracted, at least partially, despite the expanding force constantly exerted by the springs 31. As an example, the drilling string B and tool are usually elevated to some extent whenever the drill string is to be raised above the slips (not shown) at the top of the well bore when another section of drill pipe has been added to the drill vstring.

The apparatus disclosed in the drawings prevents the tubular mandrel 11 from being elevated with respect to the body 15 whenever the cutters are relieved of drilling weight, as by raising them above the formation shoulder C. To accomplish this purpose, a detent or holding device is provided between the kelly portion 14 of the tubular mandrel 11 and the body 15 of the tool. As shown, the counterbore 15a of the body has a lower socket or recess 90 in which one or a plurality of detents 91 is received when the lower end of the kelly 14 engages the upper guide or washer 48. This is the position of the parts when the cutters 25 are locked in their outwardly expanded. position by the disposition of the lock portion 47 of the mandrel behind the supporting member lugs37. A plurality of circumferentially spaced detents 91 may be used. Each detent device includes a ball 91 movable within a transverse bore 92 in the flange portion 16- of the kelly. A helical compression spring 93 is disposed in each bore, bearing against the base of the latter and against the ball 91, urging the detent outwardly, and, when aligned with the lower socket or groove 90, into the latter. The socket or groove may extend circumferentially around the body, being of generally toroidal shape, having a curvature conforming -to the curvature of the ball.

6 When the mandrel 11 is in its lower position within the .body 15, as disclosed in Fig. 2 the balls 91 are in aligninent with the toroidal groove or recess 90, the springs 93 urging the balls into this groove and tending to hold them therein. The springs 93 exert sufficient force, so that once the mandrel 11 has been lowered within the body 15, to

place its lock portion 47 behind the supporting member lugs 37, the mandrel will remain in this position until a substantial upward force is imposed thereon. The mere elevation of the drill string B and the mandrel 11 will carry the body 15 upwardly with the mandrel, the lock portion 47 remaining behind the supporting member lugs 37. Accordingly, the supporting members 19 and the cutters 25 cannot retract as an incident of the raising of the cutters ,above the formation shoulder C since the detents 91 prevent the upward telescoping of the tubular mandrel 11 with respect to the body 15 of the rotary drill bit and the cutter supporting members 19.

When it is desired to withdraw the tool from the well bore, the drill string B is elevated, within the well bore. The parts will. occupy the relative positions shown in Fig. 2 until the supporting arms 23 engage a restricted diameter portion of the well bore, or the casing shoe. Such engagement will preclude further upward movement of the cutter supporting members 19 and the body 15 of the tool, for the time being, allowing an upward force to .be imposed on the drill string B and the tubular mandrel 11 sufiicient to overcome the holding force of the springs 93 tending to maintain the balls .91within the lower groove 98. Accordingly, the upper inclined surface of this groove will force the balls 91 inwardly completely out of the groove 90, and when this occurs, the mandrel 11 can shift upwardly of the body until the shoulder 16 engages the upper retaining ring 17, whereupon the cutters 25 are movableinwardly to their retracted position against the force of the springs 31, as described above, the tool then being elevated through the well casing.

If desired, an upper generally toroidal groove 94 can also be provided in the counterbore portion 15a of the body. This groove 94- is placed in such a position that when the mandrelshoulder 16 engages the retainer ring 17, the ball detent elements 91 will be in alignment with it, the springs 93 snapping the balls into the groove 94, in order to releasably and positively hold the mandrel 11 in its elevated position with respect to the body 15 of the tool, which is the position disclosed in Fig. 1. It may be desirable to employ the upper groove 94, but it can be omitted. If it is used, then following the release of the latch 78 and the outward expansion of the cutters 25 to their maximum extent, the imposition of suflicient downweight on the drill string B and tubular mandrel 11 will cause the balls 91 to engage the lower portion of the toroidal groove 94, which will force the balls 91 inwardly against the action of the springs 93, allowing the mandrel 11 to shift downwardly to its locked position,v as shown in Fig. 2, whereupon the balls 91 will be forced into the lower groove 90, releasably securing the mandrel 11 to the body 15 in its locked position behind the supporting member lugs 37.

In Fig. 5, a modified form of detent structure is provided. In place of the balland spring arrangement, the kelly flange 1.6 may be provided with a circumferential groove 95 receiving a split snap ring 96, which inherently tends to expand. This snap ring can expand into a lower groove 99a in the body counterbore 15a, or into an upper groove 94a in the body counterbore. Each groove has sides 97 which taper toward each other in a lateral outward direction, to be engaged by companion outer tapered sides 98 on the split snap ring or detent 96. When the ring is engaged in either of the grooves a or 94a, its upper and lower parallel sides 99 are engageable with the companion sides 100 of the peripheral groove in the kelly flange.

The. grooves 90a, 94a with the tapered sides 97 are appropriately located in the body 15 of the tool, so that the ring 96 can snap into the upper groove 94a, when the mandrel 11 is in its uppermost position, with its kelly flange 16 engaging the retainer ring 17, which allows the cutter supporting members 19 and cutetrs 25 to occupy the retracted position shown in Fig. l. Lowering of the mandrel 11 with respect to the body 15, to dispose its lock portion 47 behind the supporting member lugs 37, and with the lower end of the kelly 14 engaging the upper guide 48, will locate the snap ring 96 in the lower holding groove 510a.

The split snap ring detent arrangement functions in essentially the same manner as the ball detent device. With the mandrel l1 occupying its upper position with respect to the body 15, the cutters 25 are expanded outwardly until the formation shoulder C is produced. Thereafter the imposition of downweight on the drill string B and the mandrel 11 will cause the lower surface 97 of the upper groove 94a to force the split ring 96 inwardly completely out of the groove 94a, whereupon the mandrel 11 is moved downwardly to its locked position, corresponding to the position shown in Fig. 2, the snap ring 96 then expanding outwardly into the lower groove 99a, releasably locking the mandrel 11 to the body 15. In the event the mandrel 11 is to be elevated with respect to the body 15, the cutter supporting legs 23 will engage a restricted diameter bore or a casing shoe (not shown) that allows sufiicient upward force to be imposed on the drill string B and the mandrel 11, to cause the upper tapered side 97 of the lower groove 99:! to force the split snap ring 96 inwardly out of the groove 99a, allowing the mandrel it to be shifted upwardly with respect to the body 15 of the tool to its cutter retracting position, whereupon the ring 96 will again snap into the upper groove Ma.

It is, accordingly, apparent that rotary expansible drill bits have been provided, in which the cutters may be locked in their maximum outwardly expanded position by the downward shifting of the telescopic mandrel 11 within the body 15. The mandrel will remain in this position to prevent the cutters 25 from retracting, in the event drilling weight is removed from the apparatus and the drill string B elevated. The mandrel 11 is only shifted to a position allowing the cutters to retract when this action is desired, as upon the elevation and withdrawal of the entire apparatus from the well bore. can the mandrel be releasably retained in its lower position within the body, to hold the cutters locked outwardly, but it can be releasably retained in its upward position within the body to prevent its inadvertent downward movement within the body.

The inventor claims:

1. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, means for expanding and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel connectible to a drill string and slidably splined to said body, said mandrel being movable relatively downward of said body to hold said cutter means laterally outward, and releasable coengageable detent means on said body and mandrel to releasably hold said mandrel in its relative downward position with respect to said body in the absence of drilling weight on said cutter means wherein said mandrel holds said cutter means laterally outward.

2. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, means for expanding and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel connectible to a drill string and slidably splined to said body, said mandrel being movable relatively downward of said body to hold said cutter means laterally outward, and releasable coengageable detent means on said body and mandrel to releasably hold said mandrel in its relative downward position with respect to said body in the absence Not only of drilling weight on said cutter means, wherein said mandrel holds said cutter means laterally outward, said detent means also releasably holding said mandrel in its relative upward position with respect to said body wherein said mandrel allows said cutter means to retract.

3. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, means for expanding and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel connectible to a drill string and slidably splined to said body, said mandrel being movable in one longitudinal direction with respect to said body to hold said cutter means laterally outward, and releasable coengageable detent means on said body and mandrel to releasably hold said mandrel in said one longitudinal position with respect to said body in the absence of drilling weight on said cutter means wherein said mandrel holds said cutter means laterally outward.

4. A rotary well drilling bit, including a main body, cutter means mounted on said body for expansion laterally outward of said body, means for expanding and holding said cutter means laterally outward, said'expanding and holding means comprising a mandrel connectible to a drill string and slidably splined to said body, said mandrel being movable in one longitudinal direction with respect to said body to hold said cutter means laterally outward and releasable coengageable detent means on said body and mandrel to releasably hold said mandrel in said one longitudinal position with respect to said body in the absence of drilling weight on said cutter means wherein said mandrel holds said cutter means laterally outward, said detent means also releasably holding said mandrel with respect to said body in another position wherein said mandrel allows said cutter means to retract.

5. A rotary well drilling bit, including a main body, cutter means mounted on said body, means engaging said cutter means for expanding said cutter means laterally outward of said body, a mandrel connectible to a drill string and slidably splined to said body, said mandrel including a portion movable in one longitudinal direction relative to said body into engagement with said cutter means to prevent inward movement of said cutter means from its outwardly expanded position, and releasable coengageable detent means on said body and mandrel to releasably hold said mandrel in said position relative to said body in the absence of drilling weight on said cutter means wherein said mandrel holds said cutter means laterally outward.

6. A rotary well drilling bit, including a main body, cutter means mounted on said body, means engaging said cutter means for expanding said cutter means laterally outward of said body, a mandrel connectible to a drill string and slidably splined to said body, said mandrel including a portion movable downwardly with respect to said body into engagement with said cutter means to prevent inward movement of said cutter means from its outwardly expanded position, and releasable coengageable detent means on said body and mandrel to releasably hold said mandrel in its relative downward position with respect to said body in the absence of drilling weight on said cutter means wherein said mandrel holds said cutter means laterally outward.

7. A rotary well drilling bit, including a main body member, cutter means mounted on said body member for expansion laterally outward of said body member, means for expanding and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel member connectible to a drill string and slidably splined to said bodymember, said mandrel member being movable relatively downward of said body member to hold said cutter means laterally outward, one of said members having a recess therein, and spring detent means on the other of said members shiftable into said recess when said mandrel member is in its position holding said cutter means laterally outward to releasably couple said mandrel member to said body member and retain said mandrel member in such position in the absence of drilling weight on said cutter means.

8. A rotary well drilling bit, including a main body member, cutter means mounted on said body member for expansion laterally outward of said body member, means for expanding and holding said cutter means laterally outward, said expanding and holding means comprising a mandrel member connectible to a drill string and slidably splined to said body member, said mandrel member being movable relatively downward of said body member to hold said cutter means laterally outward, one of said members having longitudinally spaced upper and lower recesses therein, and spring detent means on the other of said members shiftable into one of said recesses when said mandrel member is in the position holding said cutter means laterally outward to releasably couple said mandrel member to said body member and retain said mandrel member in such position in the absence of drilling weight on said cutter means, said detent means being shiftable into said other recess to releasably couple said mandrel member in its relative upward position with respect to said body member allowing said cutter means to retract.

9. A rotary Well drilling bit, including a main body member, cutter means mounted on said body member, means engaging said cutter means for expanding said cutter means laterally outward of said body member, a mandrel member connectible to a drill string and slidably splined to said body member, said mandrel member including a portion movable downwardly relative to said body member into engagement with said cutter means to prevent inward movement of said cutter means from its outwardly expanded position, one of said members having a recess therein, and spring detent means on the other of said members shiftable into said recess when said mandrel member is in a position holding said cutter means laterally outward to releasably couple said mandrel member to said body member and retain said mandrel member in such position in the absence of drilling weight on said cutter means.

10. A rotary well drilling bit, including a main body member, cutter means mounted on said body member, means engaging said cutter means for expanding said cutter means laterally outward of said body member, a mandrel member connectible to a drill string and slidably splined to said body member, said mandrel member including a portion movable downwardly relative to said body member into engagement with said cutter means to prevent inward movement of said cutter means from its outwardly expanded position, one of said members having longitudinally spaced upper and lower recesses therein, and spring detent means on the other of said members shiftable into one of said recesses when said mandrel member is in the position holding said cutter means laterally outward to releasably couple said mandrel member to said body member and retain said mandrel member in such position in the absence of drilling weight on said cutter means, said detent means being shiftable into the other of said recesses to releasably couple said mandrel member in its relative upward position with respect to said body member allowing said cutter means to retract.

References Cited in the file of this patent UNITED STATES PATENTS 

